1. Field of the Invention
This invention relates to a torque nut having an injection-molded breakaway insert or delay stopper and to a method of manufacturing the torque nut.
2. Description of the Presently Available Technology
It is well known in the art of mine roof support to tension bolts anchored in bore holes drilled in the mine roof to reinforce the unsupported rock formation above the mine roof surface, e.g., as disclosed in U.S. patent application Ser. No. 11/064,426, filed Feb. 23, 2005, entitled “TRUSS SHOE”, which application is hereby incorporated by reference. Conventionally, a bore hole is drilled through the roof into the rock formation. The end of the bolt in the rock formation is anchored by either engagement of an expansion shell on the end of the bolt with the rock formation, or adhesively bonding the bolt by resin to the rock formation, or by utilizing a combination of an expansion shell and resin bonding to secure the roof anchor within the bore hole. Of particular interest in this discussion is the torque nut used to secure an end of the anchor in the mine roof and to secure mine roof stabilizing components on the other end of the anchor.
In general and as discussed in U.S. Pat. No. 5,064,312, which patent is hereby incorporated by reference, the technique of securing the anchor in the bore hole includes inserting a capsule into a bore hole drilled into the mine roof. The capsule contains a resin component and a catalyst component. An end of the anchor is moved into the bore hole to move the end of the anchor into contact with the resin capsule. The anchor is rotated and further moved into the bore hole to fracture the resin capsule and to mix the resin component and the catalyst component together to provide a resin, which will set and harden within the bore hole. After the resin sets, a nut is threaded onto the threaded end of the anchor extending out of the hole to the mine roof stabilizing components, e.g., a bearing plate or truss shoe against the mine roof or wall.
One technique to rotate the anchor to fracture the capsule and/or to mix the resin and catalyst is disclosed in U.S. Pat. No. 4,556,350. In general, a nut has a plug of chemical setting resinous material at an end portion of the nut and is rotated onto the threaded end of the anchor extending out of the hole. Continued rotation of the nut moves the end of the anchor and the plug into contact with one another, after which rotation of the nut rotates the anchor. After the resin hardens to secure the anchor in the bore hole, continued rotation of the nut under increased torque breaks up the plug and the nut can be rotated on the threaded end of the anchor to move the roof stabilizing components against the mine roof.
Although the nut disclosed in U.S. Pat. No. 4,556,350 is acceptable to fracture the capsule and/or to mix the resin and catalyst, there are drawbacks. More particularly, to secure the plug in the nut, the nut has to be degreased to ensure bonding of the plug to the inner surface of the nut to provide consistency of performance of the nut in the field. Further, when forming the resin plug, the nut is desirably placed on a tray treated with a release agent and the desired amount of resin poured into the nut and allowed to cure.
As can be appreciated by those skilled in the art, it would be advantageous to provide a nut having a plug, insert, or delay stopper that does not require the degreasing step, the treatment of the trays with a release agent, and storage of the nuts to cure the resin.